This took the total spent on the format to £1.17bn – while total video spend grew 47% to £1.61bn.
Smartphone video accounted for a third of the overall increase in digital adspend, which was up 14.3%, from £10.1bn to £11.6bn.
Spend on all smartphone advertising – including video, display, native and search – grew by 37.4% to £5.2bn, meaning smartphones now account for 45% of all digital adspend. This is up from 37% last year, and from just 9% five years ago.
If this trend continues, over half of digital adspend will go on smartphones in 2018. According to data from Ukom/ComScore, smartphones accounted for 59% of online time in the final quarter of 2017 – meaning share of spend still lags share of time.
Within video, spend on outstream video almost doubled to £900m, helping it overtake pre/post-roll (up 11% to £671m) as the larger video format.
Social media spend grew 38% to £2.39bn, with 83% of social budget now going to smartphones.
And of the £3.84bn spent on display advertising, 80% was traded programmatically – up from 72% in 2016.
The IPA Bellwether Report, published last week, found that digital marketing spend in the first quarter of 2018 grew at 8.7%, down from 10.9% the previous quarter.
Tim Elkington, chief digital editor at the IAB, said: "Digital has led to a change in consumer behaviour as people use their smartphone for a wider variety of things. The ad community has responded to this change – particularly the growth of mobile and video – by developing dynamic ad products that fit seamlessly into their environment.
"There have been growing pains within the industry so we’re focused on building a sustainable future for advertising through initiatives such as the IAB Gold Standard, which aims to reduce ad fraud, improve the digital ad experience and increase brand safety."